Short answers, pulled from the story.
"Marching Through Georgia" was written and composed by Henry Clay Work, an American songwriter and printer who was born in 1832 and died in 1884. Work wrote the song as a commemoration of Sherman's March to the Sea and released it around the 9th of January 1865.
"Marching Through Georgia" was released around the 9th of January 1865, just weeks after Sherman's army entered Savannah on the 21st of December 1864, concluding the March to the Sea.
Sherman came to despise "Marching Through Georgia" because it was played incessantly at public functions he attended. At the 1890 national encampment of the Grand Army of the Republic, hundreds of bands played the tune every time they passed him for seven unbroken hours. He reportedly vowed never to attend another encampment until every band in the United States had pledged not to play it in his presence.
"Marching Through Georgia" sold 500,000 copies of sheet music within 12 years of its release, making it one of the most commercially successful wartime compositions and Work's most profitable song.
"Marching Through Georgia" is written in the key of B-flat major and common time. It opens with a four-bar introduction built on a chord progression of B-flat, E-flat, B-flat, F7, and B-flat, and each verse and chorus runs eight bars.
Japanese troops sang "Marching Through Georgia" as they entered Port Arthur at the start of the Russo-Japanese War, and British soldiers stationed in India periodically used it as well. The melody was also adapted into various regional military and nationalist anthems, including the pro-Ulster hymn "Billy Boys".